Microstructured optical films comprising polymerizable ultraviolet absorber

ABSTRACT

Polymerizable resin compositions and microstructures comprising the reaction product of such polymerizable resin compositions are described. The microstructures comprise the reaction product of a polymerizable resin composition comprising an organic portion having a refractive index of at least 1.56 wherein the polymerizable resin composition comprises a polymerizable ultraviolet absorbing compound.

BACKGROUND

Certain microreplicated optical products, such as described in U.S. Pat.Nos. 5,175,030 and 5,183,597, are commonly referred to as a “brightnessenhancing films”.

Brightness enhancing films are currently used in various (e.g. LCD)hand-held display devices, such as cell phones, PDAs, and MP3 players,to increase battery life and display brightness.

U.S. Pat. No. 7,586,566 describes a brightness enhancing film suitablefor use in a display device is disclosed herein. The film comprises afirst polymeric layer having a microstructured surface, wherein themicrostructured surface comprises an array of prism elements, and asecond polymeric layer disposed adjacent to the first polymeric layer onthe opposite side of the microstructured surface, wherein at least oneof the first and second polymeric layers comprises a UV absorber thatabsorbs UV light and transmits visible light, such that the brightnessenhancing film has an internal percent transmission of at least 95% at410 nm, and at most 25% at 380 nm. Also disclosed herein is a brightnessenhancing film wherein the UV absorber is in a third layer disposedbetween the first and second layers. The brightness enhancing films maybe used in display devices such as LCD-TVs.

SUMMARY

In some embodiments, microstructured films comprising a polymerizedmicrostructured surface are described. In one embodiment, themicrostructures comprise the reaction product of a polymerizable resincomposition comprising an organic portion having a refractive index ofat least 1.56 wherein the polymerizable resin composition comprises apolymerizable ultraviolet absorbing compound.

In other embodiments, polymerizable resin compositions andmicrostructures comprising the reaction product of such polymerizableresin compositions are described.

In one embodiment, the polymerizable resin composition comprises

i) at least one aromatic (meth)acrylate aromatic monomer or oligomerwherein the monomer or oligomer comprises sulfur, naphthyl, fluorene, ora mixture thereof; andii) an ultraviolet absorbing compound comprising a core structureselected from the group consisting of hydroxy-benzophenone,hydroxy-phenyl-benzotriazole, hydroxy-phenyl-triazine, and a substituentbonded to the core structure, wherein the substituent comprises a(meth)acrylate end group.

In another embodiment, the polymerizable resin composition comprises

i) 1% to 20% by weight of one or more (meth)acrylate monomersrepresented by the formula

UVA-L_(v)-A

wherein,UVA is a substituted or unsubstituted core structure selected from thegroup consisting of

L_(v) is a linking group, covalently bonding UVA to A,and A is a (meth)acrylate group; andii) a substantially non-halogenated (meth)acrylate monomer or oligomerhaving a refractive index of at least 1.585.

DETAILED DESCRIPTION

Presently described are polymerizable resin compositions for use inmaking microstructured optical film articles, especially brightnessenhancing films. The microstructured (e.g. brightness enhancing) filmsdescribed herein comprise a polymerized microstructured surface whereinthe microstructures comprise the reaction product of a polymerizableresin composition comprising a polymerizable ultraviolet absorbingcompound.

The ultraviolet absorbing compound typically comprises a core structurecomprising an ultraviolet absorbing group. The ultraviolet absorbingcompound further comprises one or more substituents bonded to the corestructure. At least one of the substituents comprises a (meth)acrylateend group. The ultraviolet absorbing compound is typically a mono(meth)acrylate compound, having a single polymerizable (meth)acrylategroup.

The polymerizable ultraviolet absorbing compound can be represented bythe general

UVA-L_(v)-A

wherein UVA represents an ultraviolet absorbing group, Lv is a linkinggroup covalently bonding UVA to A, and A is a (meth)acrylate grouprepresented by

wherein R1 is methyl or H.

Various ultraviolet absorbing compounds are commercially availableincluding for example hydroxy-benzophenone,hydroxy-phenyl-benzotriazole, or hydroxy-phenyl-triazine. The aromaticrings of the hydroxy-benzophenone, hydroxy-phenyl-benzotriazole, orhydroxy-phenyl-triazine core structure may optionally further comprisevarious substituents, as known in the art. For example, the corestructure may comprise one or more (e.g. C₁ to C₄) alkyl groupsoptionally containing an ether linkage(s) or hydroxyl group(s).

Several starting compounds are commercially available or have beendescribed in the literature having a polymerizable hydroxyl group (—OH)that can be reacted with acrylochloride for example to convert ahydroxyl group to a substituent having a (meth)acrylate group.

The hydroxyl-benzophenone ultraviolet absorbing groups can berepresented by the general core structure:

One suitable polymerizable benzophenone ultraviolet absorbing compoundthat has been found to be suitable is1,2-(4-benzoyl-3-hydroxyphenoxy)ethyl acrylate, depicted as follows:

This polymerizable ultraviolet absorbing compound is commerciallyavailable from Aldrich.

Another representative polymerizable hydroxyl-benzophenone ultravioletabsorbing compound is

This polymerizable ultraviolet absorbing compound is commerciallyavailable from Monomer-Polymer & Dajac Laboratories, Inc.

The hydroxy-phenyl-benzotriazole ultraviolet absorbing groups can berepresented by the general core structure:

One suitable polymerizable hydroxy-phenyl-benzotriazole ultravioletabsorbing compound that has been found to be suitable is2,2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate,depicted as follows:

This polymerizable ultraviolet absorbing compound is commerciallyavailable from Aldrich and also from Ciba under the trade designation“Tinuvin R 796”.

The hydroxy-phenyl-benzotriazine ultraviolet absorbing groups can berepresented by the general formula:

One representative polymerizable hydroxy-phenyl-benzotriazineultraviolet absorbing compound is depicted as follows:

This polymerizable ultraviolet absorbing compound could be readilyprepared from the following precursor that is commercially availablefrom Ciba Specialty Chemicals Corp., Additives Division.

The polymerizable ultraviolet absorbing compound is added to thepolymerizable resin composition is an amount of at least 0.5, 1.0, 1.5,or 2 wt-%. When the polymerizable ultraviolet absorbing compound hashigh refractive index, (e.g. of at least 1.58) the amount ofpolymerizable ultraviolet absorbing compound can range up to as much as20 wt-%. Typically, however, the polymerizable ultraviolet absorbingcompound is added at a sufficient, but minimal concentration to reducethe yellowness that would otherwise occur after extended exposure toultraviolet. The concentration of polymerizable ultraviolet absorbingcompound is typically no greater than about 10 wt-% and more typicallyno greater than about 5 wt-%.

The polymerizable resin may optionally further comprise a lightstabilizer, such as a hindered amine light stabilizer (HALS). Suchcompounds are typically derivatives of 2,2,6,6,-tetramethyl piperidine.One preferred HALS is commercially available from Ciba under the tradedesignation “Tinuvin 152”, having the following structure.

However, the polymerizable resin preferably comprises no greater than 1%by weight of non-polymerizable additives other than photoinitiator. Morepreferably, the polymerizable resin is free of non-polymerizableadditives other than photoinitiator and thus free of non-reactivecomponents that can migrate to the film surface over time.

In some embodiments, the polymerizable resin composition issubstantially free of inorganic nanoparticles. In this embodiment, thepolymerizable resin composition and organic component are one in thesame. In other embodiments, the polymerizable resin compositioncomprises surface modified inorganic nanoparticles. In such embodiments,“polymerizable composition” refers to the total composition, i.e. theorganic component and surface modified inorganic nanoparticles.

The organic component and the polymerizable resin composition arepreferably substantially solvent free. “Substantially solvent free”refer to the polymerizable composition having less than 5 wt-%, 4 wt-%,3 wt-%, 2 wt-%, 1 wt-% and 0.5 wt-% of non-polymerizable (e.g. organic)solvent. The concentration of solvent can be determined by knownmethods, such as gas chromatography (as described in ASTM D5403).Solvent concentrations of less than 0.5 wt-% are preferred.

The components of the organic component are preferably chosen such thatthe polymerizable resin composition has a low viscosity. In someembodiments, the viscosity of the organic component is less than 1000cps and typically less than 900 cps at the coating temperature. Theviscosity of the organic component may be less than 800 cps, less than700 cps, less than 600 cps, or less than 500 cps at the coatingtemperature. As used herein, viscosity is measured (at a shear rate upto 1000 sec-1) with 25 mm parallel plates using a Dynamic StressRheometer. Further, the viscosity of the organic component is typicallyat least 10 cps, more typically at least 50 cps at the coatingtemperature.

The coating temperature typically ranges from ambient temperature, 77°F. (25° C.) to 180° F. (82° C.). The coating temperature may be lessthan 170° F. (77° C.), less than 160° F. (71° C.), less than 150° F.(66° C.), less than 140° F. (60° C.), less than 130° F. (54° C.), orless than 120° F. (49° C.). The organic component can be a solid orcomprise a solid component provided that the melting point in thepolymerizable composition is less than the coating temperature. Theorganic components described herein are preferably liquids at ambienttemperature.

The organic component has a refractive index of at least 1.54, 1.55,1.56, 1.57, 1.58, 1.59, 1.60, 1.61, or 1.62. The polymerizablecomposition including high refractive index nanoparticles can have arefractive index as high as 1.70. (e.g. at least 1.61, 1.62, 1.63, 1.64,1.65, 1.66, 1.67, 1.68, or 1.69). High transmittance in the visiblelight spectrum is also typically preferred.

The polymerizable composition is energy curable in time scalespreferably less than five minutes (e.g. for a brightness enhancing filmhaving a 75 micron thickness). The polymerizable composition ispreferably sufficiently crosslinked to provide a glass transitiontemperature that is typically greater than 45° C. The glass transitiontemperature can be measured by methods known in the art, such asDifferential Scanning Calorimetry (DSC), modulated DSC, or DynamicMechanical Analysis. The polymerizable composition can be polymerized byconventional free radical polymerization methods.

As described for example in U.S. Pat. No. 5,932,626, one importantproperty of an optical material is its index of refraction, becauseindex of refraction is related to how effectively an optical materialcan control the flow of light. There exists a continuing need foroptical materials and optical products that exhibit a high index ofrefraction. With respect specifically to brightness enhancement films,the index of refraction is related to the brightness gain or “gain”produced by the brightness enhancement film. Gain is a measure of theimprovement in brightness of a display due to the brightness enhancementfilm, and is a property of the optical material (e.g., its index ofrefraction), and also of the geometry of the brightness enhancementfilm; as gain increases viewing angle will typically decrease. A highgain is desired for a brightness enhancement film because improved gainprovides an effective increase in the brightness of a backlit display.Improved brightness means that the electronic product can operate moreefficiently by using less power to light the display, thereby reducingpower consumption, placing a lower heat load on its components, andextending the lifetime of the product. Thus, because of theseadvantages, there exists a continuing need to find optical products toprovide improved levels of brightness gain, with even very small,seemingly incremental improvements being quite significant.

One way to increase the refractive index of a polymerizable resincomposition is to employ various brominated (meth)acrylate monomers, asdescribed in the art. However, the polymerizable resin compositionsdescribed herein are preferably non-brominated, meaning that thepolymerizable components utilized do not comprise bromine substituents.In some embodiments, the polymerizable resin compositions arenon-halogenated. However, a detectable amount, i.e. less than 1 wt-% (asmeasured according to Ion Chromatography) of (e.g. bromine) halogen maybe present as a contaminant.

Although polymerizable ultraviolet absorbing compound can be added tomost any polymerizable resin composition, it has been found that theaddition of such compounds substantially benefits polymerizable resincomposition comprising certain classes of high refractive index(meth)acrylate monomers that are particularly susceptible to yellowing.In some embodiments, aromatic (meth)acrylate monomers and oligomersparticularly susceptible to yellowing can be characterized as having arefractive index of least 1.585.

The yellowness of the microstructured (e.g. brightness enhancing)optical film can be determined by measuring the change in yellowness, orΔb*, as is known in the CIE L*a*b* color space, developed by theCommission Internationale de l'Eclairage in 1976. A widely used methodfor measuring and ordering color, CIE L*a*b* color space is athree-dimensional space in which a color is defined as a location in thespace using the terms L,*, a*, and b*. L* is a measure of the lightnessof a color and ranges from zero (black) to 100 (white) and may bevisualized as the z-axis of a typical three-dimensional plot having x-,y- and z-axes. The terms a* and b* define the hue and chroma of a colorand may be visualized as the x- and y-axes, respectively. The term a*ranges from a negative number (green) to a positive number (red), andthe term b* ranges from a negative number (blue) to a positive number(yellow). Thus, b*, as used herein, relates to the yellowness of anarticle. For a complete description of color measurement, see “MeasuringColor”, 2nd Edition by R. W. G. Hunt, published by Ellis Horwood Ltd.,1991. In general, b* for the brightness enhancing film is no greaterthan 2.5, otherwise it appears too yellow.

One class of monomers that has been found to be particularly susceptibleto yellowing are fluorene-containing monomers. One particularfluorene-containing (meth)acrylate monomer that has been described foruse as a high refractive index reactive diluent is9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene (NK Ester A-BPEF),available from Shin-Nakamura. The structure of this monomer is shown asfollows:

Another class of monomers that have been found to be particularlysusceptible to yellowing are naphthyl-containing aromatic monomers. Oneparticular naphthyl-containing (meth)acrylate monomer that has beendescribed for use as a high refractive index reactive diluent is2-(1-napthyloxy)-1-ethyl acrylate, as described in U.S. Pat. No.6,953,623. The structure of this monomer is shown as follows:

Other naphthyl-containing (meth)acrylate monomers include for example2-naphthylthio ethyl acrylate; 1-naphthylthio ethyl acrylate; andnaphthyloxy ethyl acrylate.

Another class of monomers that have been found to be particularlysusceptible to yellowing are sulfur-containing aromatic monomers andoligomers.

The polymerizable resin comprises a mixture of ethylenically unsaturatedcomponents. The mixture includes a major amount of at least onedifunctional aromatic (meth)acrylate monomer or oligomer and at leastone monfunctional aromatic (meth)acrylate diluent.

The polymerizable UV absorber is particularly useful when thedi(meth)acrylate monomer is a sulfur-containing aromatic monomer, anapthyl-containing aromatic monomer, a fluorene-containing monomer, ormixture thereof. Alternatively, the polymerizable UV absorber is alsoparticularly useful when the di(meth)acrylate monomer is free of suchgroups that are highly susceptible to yellowing, yet the polymerizableresin comprises a mono(meth)acrylate monomer that is a sulfur-containingaromatic monomer, a napthyl-containing aromatic monomer, afluorene-containing monomer, or mixture thereof. Further, thepolymerizable UV absorber is also particularly when the polymerizableresin comprises both a di(meth)acrylate monomer and mono(meth)acrylatemonomer, each containing groups that are susceptible to yellowing.

The (meth)acrylate diluent has a lower molecular weight and thus asubstantially lower viscosity than that of the di(meth)acrylatecomponent, i.e. less than 300 cps at 25° C. In some embodiments, theviscosity of the (meth)acrylate diluent is less than 250 cps, 200 cps,150 cps, 100 cps, or 50 cps at 25° C. The inclusion of one or more(meth)acrylate diluents improves the processability by reducing theviscosity of the polymerizable resin composition allowing for fasterfilling of the cavities of the microstructured tool.

In some embodiments, the aromatic monomer is a bisphenoldi(meth)acrylate, i.e. the reaction product of a bisphenol A diglycidylether and acrylic acid. Although, bisphenol A is most widely available,it is appreciated that other bisphenol diglycidyl ethers, such asbisphenol F digycidyl could also be used. In other embodiments, themonomer is an aromatic epoxy di(meth)acrylate oligomer derived from adifferent starting monomer.

Regardless of the starting monomers, the polymerizable compositionpreferably comprises at least one aromatic difunctional (meth)acrylatemonomer.

In some embodiments the difunctional (meth)acrylate monomer is afluorene-containing monomer, such as previously described.

In other embodiments, the difunctional (meth)acrylate monomer thatcomprises a major portion having the following general structure:

wherein Z is independently —C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or—S(O)₂—, each Q is independently O or S. L is a linking group. L mayindependently comprise a branched or linear C₂-C₆ alkyl group and nranges from 0 to 10. More preferably L is C₂ or C₃ and n is 0, 1, 2 or3. The carbon chain of the alkyl linking group may optionally besubstituted with one or more hydroxy groups. For example L may be—CH₂CH(OH)CH₂— Typically, the linking groups are the same. R1 isindependently hydrogen or methyl.

The di(meth)acrylate monomer may be synthesized or purchased. As usedherein, major portion refers to at least 50-75 wt-% of the monomercontaining the specific structure(s) just described. It is commonlyappreciated that other reaction products are also typically present as abyproduct of the synthesis of such monomers.

Preferred di(meth)acrylate aromatic epoxy oligomers and bisphenoldi(meth)acrylate monomers, described herein, have a molecular weight(i.e. the calculated molecular weight of the major molecule) greaterthan 450 g/mole. Typically the molecular weight is less than 1600g/mole.

In other embodiments, the difunctional (meth)acrylate monomer is atriphenyl monomer such as described in WO2008/112452; incorporatedherein by reference.

For embodiments wherein the polymerizable resin composition issubstantially free of inorganic nanoparticles, the polymerizable resincomposition typically comprises one or more of such monomers in anamount of at least 50 wt-%. For embodiments wherein the polymerizableresin composition further comprises substantial amount of inorganicnanoparticles, the organic component typically comprises at least 5 wt-%and no greater than about 20 wt-% of di(meth)acrylate monomer. Thepolymerizable resin composition may comprise a single bisphenoldi(meth)acrylate monomer, two or more bisphenol di(meth)acrylatemonomer(s), a single aromatic epoxy di(meth)acrylate oligomer, two ormore aromatic epoxy di(meth)acrylate oligomers, as well as variouscombinations of at least one bisphenol di(meth)acrylate in combinationwith at least one aromatic epoxy di(meth)acrylate.

In some embodiments, the polymerizable resin composition comprises atleast 65 wt-% (66 wt-%, 67 wt-%, 68 wt-%, 69 wt-%), at least 70 wt-% (71wt-%, 72 wt-%, 73 wt-%, 74 wt-%), or at least 75 wt-% of suchdi(meth)acrylate) monomer(s) and/or oligomer(s).

Various (meth)acrylated aromatic epoxy oligomers are commerciallyavailable. For example, (meth)acrylated aromatic epoxy, (described as amodified epoxy acrylates), are available from Sartomer, Exton, Pa. underthe trade designation “CN118”, and “CN115”. (Meth)acrylated aromaticepoxy oligomer, (described as an epoxy acrylate oligomer), is availablefrom Sartomer under the trade designation “CN2204”. Further, a(meth)acrylated aromatic epoxy oligomer, (described as an epoxy novolakacrylate blended with 40% trimethylolpropane triacrylate), is availablefrom Sartomer under the trade designation “CN112C60”. One exemplaryaromatic epoxy acrylate is commercially available from Sartomer underthe trade designation “CN 120” (reported by the supplier to have arefractive index of 1.5556, a viscosity of 2150 at 65° C., and a Tg of60° C.).

One exemplary bisphenol A ethoxylated diacrylate monomer is commerciallyavailable from Sartomer under the trade designations “SR602” (reportedto have a viscosity of 610 cps at 20° C. and a Tg of 2° C.). Anotherexemplary bisphenol A ethoxylated diacrylate monomer is as commerciallyavailable from Sartomer under the trade designation “SR601” (reported tohave a viscosity of 1080 cps at 20° C. and a Tg of 60° C.).

For embodiments wherein the polymerizable resin composition issubstantially free of inorganic nanoparticles, the total amount of(meth)acrylate diluent(s) can be at least 5 wt-%, 10 wt-%, 15 wt-%, 20wt-%, or 25 wt-% of the polymerizable composition. The total amount of(meth)acrylate diluents(s) is typically no greater than 40 wt-%, andmore typically no greater than about 35 wt-%. For embodiments whereinthe polymerizable resin composition further comprises substantial amountof inorganic nanoparticles, the total amount of (meth)acrylatediluent(s) of the organic component can range up to 90 wt-%, but ittypically no greater than 75 wt-%.

In some embodiments, a multi-functional (meth)acrylate component may beemployed as a diluent. For example, tetraethylene glycol diacrylate suchas commercially available from Sartomer under the trade designation SR268 has been found to be a suitable diluent. Other suitablemulti-functional diluents include SR351, trimethylol propane triacrylate(TMPTA).

When one or more aromatic (e.g. monofunctional) (meth)acrylatemonomer(s) are employed as the diluent, such diluent can concurrentlyraise the refractive index of the polymerizable resin composition.Suitable aromatic monofunctional (meth)acrylate monomers typically havea refractive index of at least 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56,1.57, 1.58 or 1.59.

Aromatic (e.g. monofunctional) (meth)acrylate monomers typicallycomprise a phenyl, biphenyl, cumyl, or naphthyl group.

Suitable monomers include phenoxyethyl (meth)acrylate;phenoxy-2-methylethyl (meth)acrylate; phenoxyethoxyethyl (meth)acrylate,3-hydroxy-2-hydroxypropyl (meth)acrylate; benzyl (meth)acrylate; phenoxy2-methylethyl acrylate; phenoxyethoxyethyl acrylate; 3-phenoxy-2-hydroxypropyl acrylate; and phenyl acrylate.

In some embodiments, the polymerizable compositions comprise one or moremonofunctional biphenyl monomer(s).

Monofunctional biphenyl monomers comprise a terminal biphenyl group(wherein the two phenyl groups are not fused, but joined by a bond) or aterminal group comprising two aromatic groups joined by a linking group(e.g. Q). For example, when the linking group is methane, the terminalgroup is a biphenylmethane group. Alternatively, wherein the linkinggroup is —(C(CH₃)₂—, the terminal group is 4-cumyl phenyl. Themonofunctional biphenyl monomer(s) also comprise a single ethylenicallyunsaturated group that is preferably polymerizable by exposure to (e.g.UV) radiation. The monofunctional biphenyl monomer(s) preferablycomprise a single (meth)acrylate group. Acrylate functionality istypically preferred. In some aspects, the biphenyl group is joineddirectly to the ethylenically unsaturated (e.g. (meth)acrylate) group.An exemplary monomer of this type is 2-phenyl-phenyl acrylate. Thebiphenyl mono(meth)acrylate or monomer may further comprise a (e.g. 1 to5 carbon) alkyl group optionally substituted with one or more hydroxylgroups. An exemplary species of this type is 2-phenyl-2-phenoxyethylacrylate.

In one embodiment, a monofunctional biphenyl (meth)acrylate monomer isemployed having the general formula:

wherein R1 is H or CH₃;

X is O or S;

n ranges from 0 to 10 (e.g. n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10); and

L is an alkyl group having 1 to 5 carbon atoms (i.e. methyl, ethyl,propyl, butyl, or pentyl), optionally substituted with hydroxy.

In another embodiment, the monofunctional biphenyl (meth)acrylatemonomer has the general formula:

wherein R1 is H or CH₃;

X is O or S;

Q is selected from —(C(CH₃)₂—, —CH₂, —C(O)—, —S(O)—, and —S(O)₂—;

n ranges from 0 to 10 (e.g. n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10); and

L is an alkyl group having 1 to 5 carbon atoms (i.e. methyl, ethyl,butyl, or pentyl), optionally substituted with hydroxy.

Some specific monomers that are commercially available from Toagosei Co.Ltd. of Japan, include for example 2-phenyl-phenyl acrylate availableunder the trade designation “TO-2344”, 4-(-2-phenyl-2-propyl)phenylacrylate available under the trade designation “TO-2345”, ethoxylatedp-cumylphenol acrylate available under the trade designation “M-110”,and 2-phenyl-2-phenoxyethyl acrylate, available under the tradedesignation “TO-1463”.

Various combinations of aromatic monofunctional (meth)acrylate monomerscan be employed. For example, a (meth)acrylate monomer comprising aphenyl group may be employed in combination with one or more(meth)acrylate monomers comprising a biphenyl group. Further, twodifferent biphenyl (meth)acrylate monomer may be employed.

The polymerizable resin may optionally comprise up to 35 wt-% of variousother non-brominated or non-halogenated ethylenically unsaturatedmonomers. For example, when the (e.g. prism) structures are cast andphotocured upon a polycarbonate preformed polymeric film thepolymerizable resin composition may comprise one or moreN,N-disubstituted (meth)acrylamide monomers. These includeN-alkylacrylamides and N,N-dialkylacrylamides, especially thosecontaining C₁₋₄ alkyl groups. Examples are N-isopropylacrylamide,N-t-butylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide,N-vinyl pyrrolidone and N-vinyl caprolactam.

The polymerizable resin composition may also optionally comprise up to15 wt-% of a non-aromatic crosslinker that comprises at least three(meth)acrylate groups. Suitable crosslinking agents include for examplepentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,trimethylolpropane tri(methacrylate), dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate,trimethylolpropane ethoxylate tri(meth)acrylate, glyceryltri(meth)acrylate, pentaerythritol propoxylate tri(meth)acrylate, andditrimethylolpropane tetra(meth)acrylate. Any one or combination ofcrosslinking agents may be employed. Since methacrylate groups tend tobe less reactive than acrylate groups, the crosslinker(s) are preferablyfree of methacrylate functionality.

Various crosslinkers are commercially available. For example,pentaerythritol triacrylate (PETA) is commercially available fromSartomer Company, Exton, Pa. under the trade designation “SR444”; fromOsaka Organic Chemical Industry, Ltd. Osaka, Japan under the tradedesignation “Viscoat #300”; from Toagosei Co. Ltd., Tokyo, Japan underthe trade designation “Aronix M-305”; and from Eternal Chemical Co.,Ltd., Kaohsiung, Taiwan under the trade designation “Etermer 235”.Trimethylol propane triacrylate (TMPTA) is commercially available fromSartomer Company under the trade designations “SR351”. TMPTA is alsoavailable from Toagosei Co. Ltd. under the trade designation “AronixM-309”. Further, ethoxylated trimethylolpropane triacrylate andethoxylated pentaerythritol triacrylate are commercially available fromSartomer under the trade designations “SR454” and “SR494” respectively.

It is typically preferred, however, that the composition issubstantially free (e.g. less than 1-2 wt-%) of (meth)acrylate monomerand oligomers that comprise three of more (meth)acrylate groups.

The UV curable polymerizable compositions comprise at least onephotoinitiator. A single photoinitiator or blends thereof may beemployed in the brightness enhancement film of the invention. In generalthe photoinitiator(s) are at least partially soluble (e.g. at theprocessing temperature of the resin) and substantially colorless afterbeing polymerized. The photoinitiator may be (e.g. yellow) colored,provided that the photoinitiator is rendered substantially colorlessafter exposure to the UV light source.

Suitable photoinitiators include monoacylphosphine oxide andbisacylphosphine oxide. Commercially available mono or bisacylphosphineoxide photoinitiators include 2,4,6-trimethylbenzoybiphenylphosphineoxide, commercially available from BASF (Charlotte, N.C.) under thetrade designation “Lucirin TPO”; ethyl-2,4,6-trimethylbenzoylphenylphosphinate, also commercially available from BASF under the tradedesignation “Lucirin TPO-L”; andbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide commercially availablefrom Ciba Specialty Chemicals under the trade designation “Irgacure819”. Other suitable photoinitiators include2-hydroxy-2-methyl-1-phenyl-propan-1-one, commercially available fromCiba Specialty Chemicals under the trade designation “Darocur 1173” aswell as other photoinitiators commercially available from Ciba SpecialtyChemicals under the trade designations “Darocur 4265”, “Irgacure 651”,“Irgacure 1800”, “Irgacure 369”, “Irgacure 1700”, and “Irgacure 907”.

The photoinitiator can be used at a concentration of about 0.1 to about10 weight percent. More preferably, the photoinitiator is used at aconcentration of about 0.5 to about 5 wt-%. Greater than 5 wt-% isgenerally disadvantageous in view of the tendency to cause yellowdiscoloration of the brightness enhancing film. Other photoinitiatorsand photoinitiator may also suitably be employed as may be determined byone of ordinary skill in the art.

Surfactants such as fluorosurfactants and silicone based surfactants canoptionally be included in the polymerizable composition to reducesurface tension, improve wetting, allow smoother coating and fewerdefects of the coating, etc.

Surface modified (e.g. colloidal) nanoparticles can be present in thepolymerized structure in an amount effective to enhance the durabilityand/or refractive index of the article or optical element. In someembodiments, the total amount of surface modified inorganicnanoparticles can be present in the polymerizable resin or opticalarticle in an amount of at least 10 wt-%, 20 wt-%, 30 wt-% or 40 wt-%.The concentration is typically less than to 70 wt-%, and more typicallyless than 60 wt-% in order that the polymerizable resin composition hasa suitable viscosity for use in cast and cure processes of makingmicrostructured films.

The size of such particles is chosen to avoid significant visible lightscattering. It may be desirable to employ a mixture of inorganic oxideparticle types to optimize an optical or material property and to lowertotal composition cost. The surface modified colloidal nanoparticles canbe oxide particles having a (e.g. unassociated) primary particle size orassociated particle size of greater than 1 nm, 5 nm or 10 nm. Theprimary or associated particle size is generally and less than 100 nm,75 nm, or 50 nm. Typically the primary or associated particle size isless than 40 nm, 30 nm, or 20 nm. It is preferred that the nanoparticlesare unassociated. Their measurements can be based on transmissionelectron microscopy (TEM). The nanoparticles can include metal oxidessuch as, for example, alumina, zirconia, titania, mixtures thereof, ormixed oxides thereof. Surface modified colloidal nanoparticles can besubstantially fully condensed.

Fully condensed nanoparticles (with the exception of silica) typicallyhave a degree of crystallinity (measured as isolated metal oxideparticles) greater than 55%, preferably greater than 60%, and morepreferably greater than 70%. For example, the degree of crystallinitycan range up to about 86% or greater. The degree of crystallinity can bedetermined by X-ray diffraction techniques. Condensed crystalline (e.g.zirconia) nanoparticles have a high refractive index whereas amorphousnanoparticles typically have a lower refractive index.

Zirconia and titania nanoparticles can have a particle size from 5 to 50nm, or 5 to 15 nm, or 8 nm to 12 nm. Zirconia nanoparticles can bepresent in the durable article or optical element in an amount from 10to 70 wt-%, or 30 to 60 wt-%. Zirconias for use in composition andarticles of the invention are available from Nalco Chemical Co. underthe trade designation “Nalco OOSSOO8” and from Buhler AG Uzwil,Switzerland under the trade designation “Buhler zirconia Z-WO sol”.

The zirconia particles can be prepared using hydrothermal technology asdescribed in U.S. Pat. No. 7,241,437. The nanoparticles are surfacemodified. Surface modification involves attaching surface modificationagents to inorganic oxide (e.g. zirconia) particles to modify thesurface characteristics. The overall objective of the surfacemodification of the inorganic particles is to provide resins withhomogeneous components and preferably a low viscosity that can beprepared into films (e.g. using cast and cure processes) with highbrightness.

The nanoparticles are often surface-modified to improve compatibilitywith the organic matrix material. The surface-modified nanoparticles areoften non-associated, non-agglomerated, or a combination thereof in anorganic matrix material. The resulting light management films thatcontain these surface-modified nanoparticles tend to have high opticalclarity and low haze. (See for example WO2007/059228 and WO2008/121465;incorporated herein by reference)

A common way of measuring the effectiveness of such recycling of lightis to measure the gain of an optical film. As used herein, “relativegain”, is defined as the on-axis luminance, as measured by the testmethod described in the examples, when an optical film (or optical filmassembly) is placed on top of the light box, relative to the on-axisluminance measured when no optical film is present on top of the lightbox. This definition can be summarized by the following relationship:

Relative Gain=(Luminance measured with optical film)/(Luminance measuredwithout optical film)

As described in U.S. Pat. No. 5,183,597 (Lu) and U.S. Pat. No. 5,175,030(Lu et al.), a microstructure-bearing article (e.g. brightness enhancingfilm) can be prepared by a casting and curing method. Such methodincludes the steps of filling the (e.g. microprismatic) cavities of amaster negative microstructured molding surface and curing thecomposition between a preformed (e.g. optically transparent) base andthe master. The master can be metallic, such as nickel, nickel-platedcopper or brass, or can be a thermoplastic material that is stable underthe polymerization conditions, and that preferably has a surface energythat allows clean removal of the polymerized material from the master.One or more the surfaces of the base film can optionally be primed orotherwise be treated to promote adhesion of the optical layer to thebase.

Brightness enhancing films generally enhance on-axis luminance (referredherein as “brightness”) of a lighting device. Brightness enhancing filmscan be light transmissible, microstructured films. The microstructuredtopography can be a plurality of prisms on the film surface such thatthe films can be used to redirect light through reflection andrefraction. The height of the prisms typically ranges from about 1 toabout 75 microns. When used in an optical display such as that found inlaptop computers, watches, etc., the microstructured optical film canincrease brightness of an optical display by limiting light escapingfrom the display to within a pair of planes disposed at desired anglesfrom a normal axis running through the optical display. As a result,light that would exit the display outside of the allowable range isreflected back into the display where a portion of it can be “recycled”and returned back to the microstructured film at an angle that allows itto escape from the display. The recycling is useful because it canreduce power consumption needed to provide a display with a desiredlevel of brightness.

The brightness enhancing film of the invention generally comprises a(e.g. preformed polymeric film) base layer and an optical layer. Theoptical layer comprises a linear array of regular right prisms. Eachprism has a first facet and a second facet. The prisms are formed onbase that has a first surface on which the prisms are formed and asecond surface that is substantially flat or planar and opposite firstsurface. By right prisms it is meant that the apex angle is typicallyabout 90°. However, this angle can range from 70° to 120° and may rangefrom 80° to 100°. These apexes can be sharp, rounded or flattened ortruncated. For example, the ridges can be rounded to a radius in a rangeof 4 to 7 to 15 micrometers. The spacing between prism peaks (or pitch)can be 5 to 300 microns. For thin brightness enhancing films, the pitchis preferably 10 to 36 microns, and more preferably 18 to 24 microns.This corresponds to prism heights of preferably about 5 to 18 microns,and more preferably about 9 to 12 microns. The prism facets need not beidentical, and the prisms may be tilted with respect to each other. Therelationship between the total thickness of the optical article, and theheight of the prisms, may vary. However, it is typically desirable touse relatively thinner optical layers with well-defined prism facets.For thin brightness enhancing films on substrates with thicknesses closeto 1 mil (20-35 microns), a typical ratio of prism height to totalthickness is generally between 0.2 and 0.4.

The microstructured optical layer can have a variety of useful patternssuch as described and shown in U.S. Pat. No. 7,074,463; incorporatedherein by reference. These include regular or irregular prismaticpatterns can be an annular prismatic pattern, a cube-corner pattern orany other lenticular microstructure. A useful microstructure is aregular prismatic pattern that can act as a totally internal reflectingfilm for use as a brightness enhancement film. Another usefulmicrostructure is a corner-cube prismatic pattern that can act as aretroreflecting film or element for use as reflecting film. Anotheruseful microstructure is a prismatic pattern that can act as an opticalturning film or element for use in an optical display.

Depending on the product, the preformed polymeric base layer can have athickness ranging up to about 15 mils. The preformed polymeric filmtypically has a thickness of at least 0.5 mils (e.g. 0.6 mils, 0.7 mils,0.8 mils, 0.9 mils). In some embodiments, the thickness is no greaterthan about 3 mils. In some embodiments, the film thickness ranges fromabout 1 mil to 2 mils.

Useful polymeric film materials include, for example,styrene-acrylonitrile, cellulose acetate butyrate, cellulose acetatepropionate, cellulose triacetate, polyether sulfone, polymethylmethacrylate, polyurethane, polyester, polycarbonate, polyvinylchloride, polystyrene, polyethylene naphthalate, copolymers or blendsbased on naphthalene dicarboxylic acids, polycyclo-olefins, andpolyimides. Optionally, the base material can contain mixtures orcombinations of these materials. In an embodiment, the base may bemulti-layered or may contain a dispersed component suspended ordispersed in a continuous phase.

For some optical products such as brightness enhancement films,preferred preformed polymeric films include polyethylene terephthalate(PET) and polycarbonate. Examples of useful PET films include photogradepolyethylene terephthalate and MELINEX™ PET available from DuPont Filmsof Wilmington, Del.

Some preformed film materials can be optically active, and can act aspolarizing materials. A number of bases, also referred to herein asfilms or substrates, are known in the optical product art to be usefulas polarizing materials. Polarization of light through a film can beaccomplished, for example, by the inclusion of dichroic polarizers in afilm material that selectively absorbs passing light. Light polarizationcan also be achieved by including inorganic materials such as alignedmica chips or by a discontinuous phase dispersed within a continuousfilm, such as droplets of light modulating liquid crystals dispersedwithin a continuous film. As an alternative, a film can be prepared frommicrofine layers of different materials. The polarizing materials withinthe film can be aligned into a polarizing orientation, for example, byemploying methods such as stretching the film, applying electric ormagnetic fields, and coating techniques.

Examples of polarizing films include those described in U.S. Pat. Nos.5,825,543 and 5,783,120. The use of these polarizer films in combinationwith a brightness enhancement film has been described in U.S. Pat. No.6,111,696. A second example of a polarizing film that can be used as abase are those films described in U.S. Pat. No. 5,882,774. Filmsavailable commercially are the multilayer films sold under the tradedesignation DBEF (Dual Brightness Enhancement Film) from 3M. The use ofsuch multilayer polarizing optical film in a brightness enhancement filmhas been described in U.S. Pat. No. 5,828,488.

One preferred optical film having a polymerized microstructured surfaceis a brightness enhancing film. Brightness enhancing films generallyenhance on-axis luminance (referred herein as “brightness”) of alighting device. The microstructured topography can be a plurality ofprisms on the film surface such that the films can be used to redirectlight through reflection and refraction. The height of the prismstypically ranges from about 1 to about 75 microns. When used in anoptical display such as that found in laptop computers, watches, etc.,the microstructured optical film can increase brightness of an opticaldisplay by limiting light escaping from the display to within a pair ofplanes disposed at desired angles from a normal axis running through theoptical display. As a result, light that would exit the display outsideof the allowable range is reflected back into the display where aportion of it can be “recycled” and returned back to the microstructuredfilm at an angle that allows it to escape from the display. Therecycling is useful because it can reduce power consumption needed toprovide a display with a desired level of brightness.

The microstructured optical layer of a brightness enhancing filmgenerally comprises a plurality of parallel longitudinal ridgesextending along a length or width of the film. These ridges can beformed from a plurality of prism apexes. Each prism has a first facetand a second facet. The prisms are formed on base that has a firstsurface on which the prisms are formed and a second surface that issubstantially flat or planar and opposite first surface. By right prismsit is meant that the apex angle is typically about 90°. However, thisangle can range from 70° to 120° and may range from 80° to 100°. Theseapexes can be sharp, rounded or flattened or truncated. For example, theridges can be rounded to a radius in a range of 4 to 7 to 15micrometers. The spacing between prism peaks (or pitch) can be 5 to 300microns. The prisms can be arranged in various patterns such asdescribed in U.S. Pat. No. 7,074,463; incorporated herein by reference.

For thin brightness enhancing films, the pitch is preferably 10 to 36microns, and more preferably 18 to 24 microns. This corresponds to prismheights of preferably about 5 to 18 microns, and more preferably about 9to 12 microns. The prism facets need not be identical, and the prismsmay be tilted with respect to each other. The relationship between thetotal thickness of the optical article, and the height of the prisms,may vary. However, it is typically desirable to use relatively thinneroptical layers with well-defined prism facets. For thin brightnessenhancing films on substrates with thicknesses close to 1 mil (20-35microns), a typical ratio of prism height to total thickness isgenerally between 0.2 and 0.4.

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

The term “microstructure” is used herein as defined and explained inU.S. Pat. No. 4,576,850. Thus, it means the configuration of a surfacethat depicts or characterizes the predetermined desired utilitarianpurpose or function of the article having the microstructure.Discontinuities such as projections and indentations in the surface ofsaid article will deviate in profile from the average center line drawnthrough the microstructure such that the sum of the areas embraced bythe surface profile above the center line is equal to the sum of theareas below the line, said line being essentially parallel to thenominal surface (bearing the microstructure) of the article. The heightsof said deviations will typically be about +/−0.005 to +/−750 microns,as measured by an optical or electron microscope, through arepresentative characteristic length of the surface, e.g., 1-30 cm. Saidaverage center line can be plano, concave, convex, aspheric orcombinations thereof. Articles where said deviations are of low order,e.g., from +/−0.005+/−0.1 or, preferably, +/−0.05 microns, and saiddeviations are of infrequent or minimal occurrence, i.e., the surface isfree of any significant discontinuities, are those where themicrostructure-bearing surface is an essentially “flat” or “smooth”surface, such articles being useful, for example, as precision opticalelements or elements with a precision optical interface, such asophthalmic lenses. Articles where said deviations are of low order andof frequent occurrence include those having anti-reflectivemicrostructure. Articles where said deviations are of high-order, e.g.,from +/−0.1 to +/−750 microns, and attributable to microstructurecomprising a plurality of utilitarian discontinuities which are the sameor different and spaced apart or contiguous in a random or orderedmanner, are articles such as retroreflective cube-corner sheeting,linear Fresnel lenses, video discs and brightness enhancing films. Themicrostructure-bearing surface can contain utilitarian discontinuitiesof both said low and high orders. The microstructure-bearing surface maycontain extraneous or non-utilitarian discontinuities so long as theamounts or types thereof do not significantly interfere with oradversely affect the predetermined desired utilities of said articles.

“Index of refraction,” or “refractive index,” refers to the absoluterefractive index of a material (e.g., a monomer) that is understood tobe the ratio of the speed of electromagnetic radiation in free space tothe speed of the radiation in that material. The refractive index can bemeasured using known methods and is generally measured using an Abberefractometer or Bausch and Lomb Refractometer (CAT No. 33.46.10) in thevisible light region (available commercially, for example, from FisherInstruments of Pittsburgh, Pa.). It is generally appreciated that themeasured index of refraction can vary to some extent depending on theinstrument.

“(Meth)acrylate” refers to both acrylate and methacrylate compounds.

The term “nanoparticles” is defined herein to mean particles (primaryparticles or associated primary particles) with a diameter less thanabout 100 nm.

“Surface modified colloidal nanoparticle” refers to nanoparticles eachwith a modified surface such that the nanoparticles provide a stabledispersion.

“Stable dispersion” is defined herein as a dispersion in which thecolloidal nanoparticles do not agglomerate after standing for a periodof time, such as about 24 hours, under ambient conditions—e.g. roomtemperature (about 20-22° C.), atmospheric pressure, and no extremeelectromagnetic forces.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. Thus, for example, reference to acomposition containing “a compound” includes a mixture of two or morecompounds. As used in this specification and the appended claims, theterm “or” is generally employed in its sense including “and/or” unlessthe content clearly dictates otherwise.

Unless otherwise indicated, all numbers expressing quantities ofingredients, measurement of properties and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.”

The present invention should not be considered limited to the particularexamples described herein, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention can be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

Examples

-   UVA-1 1,2-(4-benzoyl-3-hydroxyphenoxy)ethyl acrylate, purchased from    Aldrich Chemical.-   UVA-2 2,2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl    methacrylate, purchased from Aldrich Chemical.-   CN120 Epoxy Acrylate, from Sartomer Company, Exton, Pa.; reported by    Sartomer to have a viscosity of 2150 cps at 65° C., a refractive    index of 1.5556, and a Tg of 60° C.-   1-NOEA 2-(1-Napthyloxy)-1-Ethyl Acrylate (from U.S. Pat. No.    6,953,623) with a viscosity of about 50 cps at 25° C., and a    refractive index of 1.585-   NK Ester 9,9-Bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, from    Shin-Nakamura-   A-BPEF Chemical Co., LTD in Wakayama City, Japan; reported to have a    refractive index of 1.62, and is a solid at 25° C.-   PTEA Phenylthioethyl Acrylate, from Cognis Corporation, Cincinnati,    Ohio, with a viscosity of about 10 cps at 25° C., and a refractive    index of 1.558-   TO-2344 2-phenyl-phenyl acrylate from Toagosei Co., LTD, Tokyo,    Japan; reported to have a viscosity of 90 cps at 25° C., a    refractive index of 1.583, and a Tg of 66° C.-   Darocur 4265 Photoinitiator blend of TPO and alpha-hydroxyketone,    available from Ciba Specialty Chemicals, Tarrytown, N.Y.

The following polymerizable resin compositions were each mixed togetherthoroughly in an amber jar.

TABLE 1 Polymerizable Resin Compositions Material 1 2 3 4 5 6 7 8 UVA-13 UVA-2 3 5 5 5 1-NOEA 30 30 30 30 A-BPEF 70 72 67 72 TO-2344 28 28CN120 70 67 67 67 PTEA 30 29 Darocur 4265 0.3 0.3 0.3 0.3 0.3 0.3 0.30.3

Optical Film Sample Preparation:

Brightness enhancing films samples were made using the polymerizableresin compositions above. About 3 grams of warm resin was applied to a 2mil primed PET (polyester) film, available from DuPont under the tradedesignation “Melinex 623” and placed against a microreplicated tool witha 90/24 pattern similar to the commercially available VikuitiTBEF-90/24. The PET, resin and tool were passed through a heatedlaminator set at approximately 150° F. to create a uniformly thicksample. The tool containing the film and coated resin sample was passedat 50 fpm through a Fusion UV processor containing two 600 W/in D-bulbs.The PET and cured resin were removed from the tool and cut into samples.Brightness by ET was measured. Color was measured in transmission mode.The samples were exposured to irradiation for 288 hours in anaccelerated weathering device equipped with Phillips F40 50U lamps, asdescribed in U.S. Pat. No. 7,124,651. Color was measured again, and thefinal b* and change in b* was recorded.

Table 2, below, depicts the test results of the optical films. TheComparative films, which did not contain the (meth)acrylate monomer A,showed unacceptable yellowing after weathering. The Inventive Exampleswere low in non-polymerizable, non-acrylate materials, and surprisinglyhad excellent brightness gain good color stability.

TABLE 2 Brightness Enhancing Film Results b* Resin ET ET change Refrac-Resin Gain Gain b* after after tive Non- Single Crossed weath- weath-Film Resin Index Acrylates Sheet Sheet ering ering Comp-1 1 1.57 0.3%1.64 2.61 11.5 10.4 Comp-2 2 1.60 0.3% 1.73 2.76 31.3 29.5 Comp-3 3 1.610.3% 1.72 2.85 6.2 3.8 Ex-4 4 1.57 0.3% 1.62 2.65 4.6 3.4 Ex-5 5 1.570.3% 1.64 2.65 3.1 1.9 Ex-6 6 1.57 0.3% 1.65 2.62 2.7 1.5 Ex-7 7 1.600.3% 1.73 2.80 1.7 −0.4 Ex-8 8 1.61 0.3% 1.71 2.82 1.6 −0.8

1. A microstructured film comprising a polymerized microstructuredsurface wherein the microstructures comprise the reaction product of apolymerizable resin composition comprising an organic portion having arefractive index of at least 1.56 wherein the polymerizable resincomposition comprises a polymerizable ultraviolet absorbing compound. 2.The microstructured film of claim 1 wherein the polymerizableultraviolet absorbing compound comprises a core structure selected fromthe group consisting of hydroxy-benzophenone,hydroxy-phenyl-benzotriazole, and hydroxy-phenyl-triazine.
 3. Themicrostructured film of claim 2 wherein the polymerizable ultravioletabsorbing compound comprises a substituent bonded to the core structureand the substituent comprises a (meth)acrylate end group.
 4. Themicrostructured film of claim 2 wherein the polymerizable ultravioletabsorbing compound is a monofunctional (meth)acrylate compound.
 5. Themicrostructured film of claim 1 wherein the polymerizable resincomposition comprises one or more polymerizable ultraviolet absorbingcompounds in a total amount ranging from about 1 wt-% to about 10 wt-%.6. The microstructured film of claim 1 wherein the polymerizable resinis non-brominated.
 7. The microstructured film of claim 1 wherein thepolymerizable resin is non-halogenated.
 8. The microstructured film ofclaim 1 wherein the polymerizable resin comprises at least one aromaticmonomer or oligomer having a refractive index of least 1.585.
 9. Themicrostructured film of claim 1 wherein the polymerizable resincomprises at least one (meth)acrylate aromatic monomer or oligomerwherein the monomer or oligomer comprises sulfur, naphthyl, fluorene, ora mixture thereof.
 10. The microstructured film of claim 1 wherein thepolymerizable resin comprises no greater than 1% by weight ofnon-polymerizable additives other than photoinitiator.
 11. Themicrostructured film of claim 1 wherein the polymerizable resin furthercomprises inorganic particles.
 12. The microstructured film of claim 1wherein the inorganic particles comprises zirconia.
 13. Themicrostructured film of claim 1 wherein a film having a thickness ofless than 300 microns has a b* of no greater than 5.0 after 288 hours ofaccelerated aging.
 14. The microstructured film of claim 1 wherein thefilm has a b* of no greater than 3.0 after 288 hours of acceleratedaging.
 15. The microstructured film of claim 1 wherein the film is abrightness enhancing film.
 16. A polymerizable resin compositioncomprising i) at least one aromatic (meth)acrylate monomer or oligomerwherein the monomer or oligomer comprises sulfur, naphthyl, fluorene, ora mixture thereof and ii) an ultraviolet absorbing compound comprising acore structure selected from the group consisting ofhydroxy-benzophenone, hydroxy-phenyl-benzotriazole,hydroxy-phenyl-triazine, and a substituent bonded to the core structure,wherein the substituent comprises a (meth)acrylate end group.
 17. Apolymerizable resin composition comprising i) 1% to 20% by weight of oneor more (meth)acrylate monomers represented by the formulaUVA-L_(v)-A wherein, UVA is a substituted or unsubstituted corestructure selected from the group consisting of

L_(v) is a linking group, covalently bonding UVA to A, and A is a(meth)acrylate group; and ii) a substantially non-halogenated(meth)acrylate monomer or oligomer having a refractive index of at least1.585. 18-21. (canceled)
 22. A microstructured film comprising apolymerized microstructured surface wherein the microstructures comprisethe reaction product of the polymerizable resin composition of claim 17.23. (canceled)
 24. The microstructured film of claim 22 wherein a filmhaving a thickness of less than 300 microns has a b* of no greater than5.0 after 288 hours of accelerated aging.
 25. The microstructured filmof claim 22 and wherein the polymerized microstructured surface has arefractive index of at least 1.59.